Although many fruit and vegetable names have regional variants in German, I don’t believe this is one of them. Mispeln are medlars, not to be confused with Japanese medlars or loquats, also sometimes called Mispeln in Germany – I’ve also seen the Turks selling them as nespole, which is Italian for medlar. The Oxford Book of Food says medlars are inedible until kept over winter in moist bran or sawdust.
I can understand the B for P, but the W for M seems more mysterious. Perhaps this is a chance to have the only Internet site displaying the word Wisbeln.